1. Field of the Invention
The present invention relates to an active roll control system, in which a stabilizer link having a screw gear formed on the outer circumferential surface thereof rotates by a motor, and a rack combined with the outer side of the stabilizer link is linearly translated in the axial direction of the link in response to the rotation of the stabilizer link so that a stabilizer bar fixed to the rack at one end thereof can be controlled, thereby enabling an active control of the active roll control system.
2. Description of the Related Art
In general, a suspension system of the vehicle connects the axle shaft and the body with each other, and controls vibration and shock from the road surface while driving so as not to be transferred directly to the body, thereby protecting the body and freight and also providing a comfortable ride. The suspension system comprises a chassis spring which relieves shock transferred from the road surface, a shock absorber which serves comfortable feelings by controlling the free vibration of the chassis spring, and a stabilizer which prevents rolling of the vehicle.
Here, the stabilizer is mounted on right and left lower arms, or on a strut bar. It does not operate in the case where the wheels at both sides move up and down simultaneously, but when the wheels vertically move relative to each other, it operates such that it is tilted and the resultant restoring force of the spring can reduce the tilt of the vehicle body.
Accordingly, in the case where the vehicle is tilted to one side due to the centrifugal force while turning, or both side wheels are at different heights relative to each other while driving over the bump or by rebounding, the vehicle is quickly stabilized as the stabilizer bar is twisted and provides a restoring force.
However, the conventional way of roll control, which uses only an elastic restitution of the stabilizer bar to prevent the vehicle against tilt or to make the tilted vehicle to be returned, is not so quick and accurate. A new system employing a hydraulic cylinder connected to a distal end of the stabilizer bar has been developed to solve the above problem and to provide an active roll control.
As described above, the new system for an active roll control using a hydraulic system is described in detail in Korean Patent Laid-Open Publication Nos. 1997-0069433 and 2002-0033863, which is briefed below.
As illustrated in FIG. 1, the conventional stabilizer bar 101 is connected at both ends to lower arms of the right and left sides, and the middle section thereof is supported by the chassis frame 103. Therefore, it does not operate in the case where the wheels at both sides move up and down simultaneously, but it operates when the wheels move vertically relatively to each other such that it is tilted and the resultant restoring force of the spring can reduce the tilt of the vehicle body, thereby maintaining the balance of the vehicle.
The above-described stabilizer bar 101 is connected to the lower arm 102 by a stabilizer link 106, which has the form of a simple steel rod with a ball joint formed at both ends thereof.
As illustrated in FIG. 2, it is known an improved mechanism, in which the stiffness of the stabilizer bar varies with the length of the stabilizer link. FIG. 2 shows a stiffness variable mechanism of a general hydraulic stabilizer, in which a piston rod 112 is connected to a ball joint 110 in which the stabilizer bar 101 is installed, and a cylinder 116 moving together with a piston 114 formed at the end of the piston rod 112 is linked to a ball joint 118 connected to the lower arm. The cylinder 116 is filled with oil 120 and has a neutral port 122 and top and bottom ports 124 and 126, which are fluid-communicated with each other by a bypass path 128, in which an operation check valve 130 is installed in order to control the moving state of the oil.
Also, an accumulator 132 having a gas filled therein through a diaphragm is installed in the bypass path 128. The accumulator 132 serves to adjust the volume difference in the inner space of the cylinder 116, which occurs when the piston rod moves in to and out of the cylinder 116, and also to prevent an occurring of cavitation by developing a certain level of oil pressure.
In the above stiffness variable mechanism, in the case where the speed of the piston 114 is relatively low due to the low frequency of disturbance from the lower arm, the piston 114 moves freely inside the cylinder 116, and thus no input is loaded to the stabilizer 101, so that the roll stiffness of the stabilizer is lowered. In the case where a big input beyond a stroke of the piston rod 112 is loaded, or the piston moves at the speed of the extent to close the operate check valve 130, the oil path is blocked by the operation check valve 130, and thus the piston stroke is controlled so that the stabilizer 101 returns to the normal stiffness thereof, thereby preventing the rolling.
However, the above system requires various complicated devices used for the additional hydraulic control, so that the whole system becomes complicated and results in an increased manufacturing cost.